He can be wrong. But this group have a history of talking bollocks on tax. And also love their 100bn tax gaps, as that was the amount of the tax gap in the UK when they did a big report about it 3 or 4 years ago. And it turns out that they included things like companies investing in machinery and knocking it off their tax as part of the "tax gap".
In general whenever someone comes up with a report that talks about huge massive headline figures - it's bollocks done for campaigning purposes and to get shock headlines. When you look closer you find that it's all dodgy adding up and/or dodgy selective use of statistics.
We all know that these companies are under-taxed - and over-use loopholes. So it's not that I disagree that they're a legitimate target. But there's often this pretence of something-for-nothing, that we can spend loads more on services without paying any more tax. And Tax Justice have been guilty fo that. This idea that we can have £100bn extra of spending, and someone else will pay. And that's just not true. People pay taxes, not companies.